When you want to play against other humans
There are always bots you can play with. However, if you want to play with other humans, the chances are higher if you announce you want to play on IRC (#chaosvpn on irc.hackint.org) or on the mailing list.
The server runs the PWNZ mod for OpenArena, which is a home made mod that makes many things configurable, for example the allowed weapons, strength of weapons, amount of ammo, start ammo & weapons. It can also be configured for instagib play (with any weapon). It can be configured to do railjumps (similar to rocketjumps, but with the railgun), which is nice in combination with instagib. There is a jump'n'bump mode where you can do damage by jumping on top of adversaries. There is also the option to switch to Newtonian physics, which changes how plasmabolts and rockets fly. It can also generate spawnpoints on the fly, which prevents people from constantly ambushing respawning players. More info here: http://git.sliepen.org/browse?p=oamod;a=blob;f=PWNZ